This
device uses a PIC16F819 and an LM339 to detect motion on a video signal.
The incoming video is 'clamped' using one section of the LM339, the sync
tips are detected with another section, and a 3rd section can detect VBI
or other data.

The analog video is fed directly
into the PIC at RA0. The low-resolution video is sampled from an 8 by
8 array on the screen. This was just an experiment, but seemed to actually
work very well. Unforturnately, the source file has been lost. For information
on how to read video samples and evaluate them see the Video
Switcher project.